Integrated circuits having in-situ constraints

ABSTRACT

An integrated device product having objects positioned in accordance with in-situ constraints. Said in-situ constraints comprise predetermined constraints and their local modifications. These local modifications, individually formulated for a specific pair of objects, account for on-the-spot conditions that influence the optimal positioning of the objects. The present invention improves the yield of integrated devices by adding local process modification distances to the predetermined constraints around processing hotspots thus adding extra safety margin to the device yield.

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 13/547,444, filed on Jul. 12, 2012, entitled“DESIGN RULE DATA STRUCTURE FOR DIRECTION-DEPENDENT INTEGRATED CIRCUITLAYOUT”, which is a continuation of US patent application Ser. No.12/181,483 filed on Jul. 29, 2008, entitled “METHOD AND SYSTEM FORANISOTROPIC INTEGRATED CIRCUIT LAYOUT”, now U.S. Pat. No. 8,266,557,which is a divisional of and claims priority to U.S. patent applicationSer. No. 10/907,814, filed on Apr. 15, 2005, now U.S. Pat. No.7,448,012, entitled “METHODS AND SYSTEM FOR IMPROVING INTEGRATED CIRCUITLAYOUT”, which claims priority to U.S. Provisional Patent ApplicationSer. No. 60/564,082 filed on Apr. 21, 2004, and U.S. Provisional PatentApplication Ser. No. 60/603,758 filed on Aug. 23, 2004. Above mentioneddocuments are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to integrated-circuit devicesand more particularly to integrated-circuit devices having superiormanufacturing yield.

PRIOR ART

In modern processing technology, the manufacturing yield of anintegrated circuit depends heavily on its layout construction. For agiven manufacturing process, a corresponding set of design rules areapplied during chip layout to avoid geometry patterns that can causechip failure. These design rules guarantee the yield by limiting layoutgeometry parameters such as minimum spacing, minimal line width, etc.

Existing layout construction systems apply design rules over a wide chiparea, and to entire classes of circuits. For this reason, the designrule must cover the worst case in all products. Failure to capture theabsolute worst case in all chips would lead to systematic yield failure.

In modern processing technologies such as advanced photolithography,many layout features may interact during chip processing. When theinteraction distance increases to greater than a few minimal pitches,the number of interacting features increases sharply. For this reason,the feature dependent interactions are difficult to capture with precisedesign rules. In practice, one makes global design rule sufficientlyrelax in order to guarantee the yield.

The drawback of this approach is at least two fold: firstly, it clearlywastes chip area, and secondly, finding the worst case featurecombination in all chips is a non-trivial task that consumes largeengineering resources.

Some emerging processing technologies also prefer one spatial directionto the other. Existing layout generation systems, however, use identicalminimal spacing and minimal width rules for both directions. This leadsto waste in chip area and under utilization of processing capability,since the design rules must cover the worst of the two directions.

SUMMARY OF INVENTION

The present invention relates to layout with geometric objects, and moreparticularly to a system and method for forming layout constraint toaccount for local and orientation processing dependencies.

The present invention provides a local process modification value to thebasic design rule constraint. Local process modification represents anadditional safeguard distance beyond the design rule constraintdistance. The local process modification value can be calculated fromsimulated process responses in the region of interest, with apredetermined, often empirical, equation, or from look-up data tables.The original design rule distance plus local process modificationeffectively creates a new constraint for every unique local situation.With this additional local safeguard, we can reduce the guard band indesign rule formulation and improve chip yield by eliminating processinghotspots arising from low probability local feature combinations.

The present invention provides a method that enforces the new localconstraints such that simulated local process modification and theoriginal design rule constraint work together to guarantee the chipyield.

For processing technologies with a preferred direction, the presentinvention constructs two sets of design rule constraint distances forthe two orthogonal spatial directions. It constructs layout designsystems that can read, store said constraint distances in differentmemory locations, and apply them according to the orientation of thelayout features. By doing so, the layout can fully take advantage of thedirectional dependence in processing technology.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is generally shown by way of example in the accompanyingdrawings in which:

FIG. 1 is a flow and block diagram showing a method and system inaccordance with the present invention;

FIG. 2 is a flow and block diagram for enforcing local constraints;

FIG. 3 is a schematic diagram illustrating the calculation of localprocess modification values;

FIG. 4 illustrates the layout artwork terminology;

FIG. 5 is a block diagram for generating anisotropic layout artwork;

FIG. 6 is a flow diagram for anisotropic layout generation;

FIG. 7a illustrates orientation dependent routing;

FIG. 7b illustrates orientation dependent jog insertion;

FIG. 8 is a block diagram showing a system for implementing the presentinvention.

Definition List 2 Term Definition width Distance of interior-facing edgefor a single layer space Distance of exterior-facing edge for one or twolayers overlap Distance of interior-facing edge for two layers enclosureDistance of inside edge to outside edge when the polygon of the insideedge is fully inside the polygon of the outside edge extension Distanceof inside edge to outside edge

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some preferred embodiments of the present invention will be described indetail with reference to the related drawings of FIGS. 1-8. Additionalembodiments, features and/or advantages of the invention will becomeapparent from the ensuing description or may be learned by the practiceof the invention.

The methods and apparatus described here are with respect to integratedcircuit manufacturing; however, the techniques described here can beapplied to manufacturing or design of any device that require patterntransfer from a polygon database drawing to physical materials usinglithographic and/or etch methods. Examples of these include integratedoptical devices, microelectromechanical systems (MEMS), gene chips,micromachines, disk drive heads, etc.

The following description includes the best mode presently contemplatedfor carrying out the invention. This description is not to be taken in alimiting sense, but is made merely for describing the general principlesof the invention.

The present invention is directed to methods for improving themanufacturing yield of an IC by optimizing its layout pattern.

FIG. 1 shows a block and flow diagram for the present invention. Inblock 000, the original design layout and process description are readinto the system. Said design layout comprises a plurality ofinterrelated layout objects, one or more layers, and can be flat ororganized in a hierarchical data structure comprising a plurality ofmasters, cells, and/or array instances. The relative distances betweensaid layout objects are constrained by design rule and design intent.

The process description comprises design rules, simulation models,manufacturing equipment settings, material options, empirical fittingparameter, and look-up data tables that describe the manufacturingbehavior.

Block 002 builds initial linear constraints from the input layout,design rules, and circuit requirements. In a preferred embodiment,well-known procedures, such as the shadow propagation method; is appliedto accomplish this task. A description of the procedure can be found inJurgen Doenhardt and Thomas Lengauer, “Algorithm Aspects ofOne-Dimensional Layout Compaction”, IEEE Trans. Computer-Aided design.Vol. CAD-6 no. 5 September 1987. pp. 863.

Said initial linear constraint equation takes the form AX=d_old, where Ais a matrix of coefficients; X is a vector of positional variablescomprising location of the polygon edges; and d_old is a column vectorof constraint distances. Constraint distances comprise design ruleconstraint distances and circuit specific design intent. Example of aconstraint distance is the minimal line width.

A constraint equation is expressed in the form xi−xj>dij_old, where xiand xj are locations of two interacting polygon edges in the layout, anddij_old is the constraint distance between these two edges. The elementsof matrix A in this equation are 1 and −1. The vector d_old is acollection of dij_old. The value of dij_old is given by the design ruleor by circuit requirements. For example, dij_old can be the minimalwidth of a wire as required by process capabilities. In another case, itdij_old is the width of a particular wire that is designed to carry alarge amount of current where it would be wider than the minimal wirewidth required by the process alone.

Block 004 generates local process modification values. A local processmodification to the design rule constraint distance transforms theglobal design rule constraints into location specific constraints.Individual evaluation and enforcement of the required safety margin ateach critical location enhances the manufacturing yield of a chip. In apreferred embodiment, we calculate local process modification atconstrained locations from manufacturing response variables. Details ofa preferred embodiment will be discussed in FIG. 3.

Block 006 combines local process modification value delta_dij, with theoriginal constraint distances generated in block 002. A linearconstraint equation now takes the form xi−xj>dij_new, wheredij_new=dij_old+delta_dij is defined as the local constraint distance. Acollection of dij_new values forms the local constraint distance vector,d_new. The system of equations for local constraint takes the formA*X=d_new.

Local constraint distance is a general addition to the constraintdistance specified by design rules. Therefore, it can be applied to anyphysical design system where design rule constrained layout constructionand optimization is performed.

Block 008 enforces the local constraint distance to the original layout.Preferred embodiments will be illustrated in FIG. 2.

Block 010 updates the coordinate variables in the layout according tothe solution of the enforcement procedure 008.

The present invention modifies a design rule constraint distance, whichis global in nature, with a local process modifier to account forspecific local conditions. This mechanism adds extra safeguard to thedesign rule methodology. If a design rule clean layout containslocations with poor process latitude, the local process modifierdelta_dij will be larger than that in other places. By enforcing the newlocal constraint, dij_new=dij_old+delta_dij, the layout is modified tohave better process latitude.

For example if two minimally spaced lines tend to bridge due to aparticular surrounding condition, the local process modifier willincrease the minimal spacing between them, causing the layout edges tomoved further apart during enforcement.

FIG. 2 shows a preferred embodiment for local constraint enforcement. Atthe start of the procedure, we have a system of equations for localconstraint, AX=d_new. The edge locations in the original layout arelikely to violate some of the local constraint distances.

Block 100 constructs an objective function Ct*X, where Ct is a rowvector of coefficients for achieving various optimization objectives,and X is the position variable in the layout. In a preferred embodiment,the objective function together with the linear constraint systemremoves the new violations introduced by local constraint with minimalperturbation. For example we can use the procedure described by Heng et.al. entitled “A VLSI Artwork Legalization Technique Based on a NewCriteria of Minimum Layout Perturbation”, ACM/IEEE Intl. Symp. onPhysical Design, pp. 116-121, 1997.

By receiving appropriate Ct values, we construct objective functions forwire length minimization, legalization, compaction, and other measurablemetrics of layout.

Block 102 solves the linear system problem of minimizing Ct*X, subjectto A*X=d_new. This is a standard form for a linear programming problem.We use commercial software packages such as CPLEX from ILOG can be usedfor this purpose.

Block 104 updates the layout with the solution X of the linear system.

In one-dimensional method, the flow is performed one direction at atime, first x(y) then y(x).

In two-dimension method, the flow is performed for horizontal andvertical position variables simultaneously.

In another preferred embodiment, the violations to local constraints areremoved one at a time using heuristic procedures. For example, thesingle error removal procedure described by Zhan Chen, in “Layout andLogic Techniques for Yield and Reliability Enhancement”, Ph.D. Thesis,University of Massachusetts Amherst, 1998, can be applied to fixisolated violations. It is particularly useful when processing hotspotsare few.

By enforcing new local constraints, we improve the local processlatitude. It is a function similar to optimal process correction (OPC).By enforcing local constraints, we can eliminate the need to perform OPCin large portion of layout. In a preferred embodiment, we tag locationswhere local constraint enforcement fails or the circuit tolerance isespecially tight so that a specially designed OPC system can pick upthese location tags and perform localized OPC.

Our experiments show that only small percentages of locations needs OPCafter local constraint enforcement. Therefore, the localized OPCprocedure will greatly reduce the mask complexity compared to thestandard, blanket OPC procedure performed today.

According to the present invention, we calculate the local processmodification value at a set of control points that best captures theinteraction between the edges. In a preferred embodiment, a simulationbased hotspot detection procedure is first applied to the layout. Afterthat, control points are placed on the offending polygon edges. Hotspotdetection comprises simulating the image of the layout and measuring thedifference between said image and the design intent. In a preferredembodiment, the difference is represented by the edge placement error(EPE). A processing hotspot is a location where EPE is larger than apredetermined threshold. As an example, the control points can be thesame points on the layout where EPE is evaluated.

In another preferred embodiment, we select the control points byinspecting the interaction among the edges. FIG. 3 shows two layoutrectangles 300 and 302, which can be on the same layer or on differentlayers in the layout. The constraint relation xi-xj>dij_old applies tothese two edges.

The interaction region between the right edge of 300 at xi (301) and theleft edge of 302 at xj (303) is defined by the shadow of 301 on 303, asmarked by the band between the two dashed lines, 304. We find the shadowregion by placing a hypothetical flashlight to the left of 301 andmeasure its shadow on 303, which is similar to the procedure used inconstraint generation in block 004 of FIG. 1.

After finding the interaction region, we implement a predeterminedsampling plan for laying down the control points. In FIG. 3, we place apair of control points 306 and 308, one on each edge, at the sameheight, in the middle of the shadow band. We can also use other spatialsampling plans involving a plurality of pairs of points.

After deciding the sampling points (e.g. 306 and 308 in FIG. 3), wesimulate various processing response variables at these points. In thephotolithography step of IC fabrication, said response variablesrepresent local printability and comprise edge placement error, lightintensity during photolithography exposure and its derivatives,contrast, and mask error enhancement factor. A predetermined empiricalfunction is used to calculate the local process modification value fromsaid processing response variables.

For the example in FIG. 3, we select a linear function of edge placementerror at point 306 and 308 to calculate local process modification. Edgeplacement error, (314/316 for the left/right edge) is defined as theperpendicular distance from intended edge location (xi/xj for theleft/right edge) to the simulated edge location as predicted by processsimulation, (310/312 for the left/right edge).

Once the edge placement errors are calculated for the two interactingedges, the local process modification value is expressed asw1*EPE_i+w2*EPE_j, where EPE_i 314 and EPE_j 316 are the edge placementerrors at 306 and 308 respectively, and w1 and w2 are user specifiedconstants. Local constraint for edges 301 and 303 can now be expressedas dij_new=dij_old+w1*EPE_i+w2*EPE_j.

Variations in functional forms for local process modification can beconstructed and additional process variables can be used in order tocover the specific needs of a particular application.

In another preferred embodiment, the local process modification value isobtained from a predetermined look-up data table. The key to the look-updata table is a set of geometry combinations that appear frequently inthe layout, such as the two rectangle case show in FIG. 3. Theapplication uses pattern recognition capability to identify the patternkey and search the look-up table in order to obtain appropriate localprocess modification value. This embodiment is advantageous when goodsimulation accuracy cannot be obtained, and the interaction is limitedto a short range.

The local process modifications discussed so far are microscopiccorrection to the design rule constraints. In modern processingtechnology, there are also systematic corrections to design rules on alarger scale. For example, in immersion lithography, one can utilize thepolarization property of the imaging light to achieve higher imageresolution in a preferred direction. Another example is the crystalorientation dependence in device performance. According to the presentinvention, we formulated two sets of design rule distances, one set forhorizontal dimensions and another set for vertical dimensions in orderto achieve best chip performance. We construct physical layout tools toutilize these two separate constraint distances. The optimal layout forthese technologies are anisotropic in that the horizontal and verticaldirections obey different constraints for minimal space, line width,overlap, enclosure, and extension rules. The exact definition of thesegeometry terms are listed in Definition List 1 and illustrated in FIG.4.

Design rules that have different constraint distances for horizontal andvertical directions are defined as anisotropic design rules. The layoutthat satisfy anisotropic design rules are defined as anisotropic layout.

Design rules that have the same constraint distances for horizontal andvertical directions are defined as isotropic design rules, or simplydesign rules. The layout that satisfy isotropic design rules are definedas isotropic layout.

The present invention comprises layout systems that are capable ofgenerating and optimizing layout artwork for a direction dependentprocessing technology.

In accordance with the current invention, we design a set of simple testpatterns with parameterized critical dimensions. The parameter valuesare selected such that they vary from the value when said pattern can besuccessfully fabricated to a value at which the fabrication clearlyfails. We extract the design rules by finding and recording theparameter value at which the test pattern can be successfully fabricatedunder all allowable processing conditions, i.e. the process window.

In a preferred embodiment, two separate sets of test patterns arefabricated. One set comprises geometries oriented along the verticaldirection. The other set comprises geometries oriented along thehorizontal direction. For example, one set has line and space gratingsrunning along the vertical direction; the other set has the same runningalong horizontal direction. The variable parameters in this example areline width and space width. Extracted design rules from this set of testpatterns represent distance constraints for line width and space widthin horizontal and vertical directions.

For a direction dependent processing technology, the present inventionextracts two distinctive sets of constraint parameters to form ananisotropic design rule set.

FIG. 5 shows a flow diagram for generating optimal layout for adirection dependent processing technology. Starting with design databasethat contains the circuit netlist and performance target (500), we applya set of software tools (501) to create a polygonal layout forfabrication. These tools comprise layout editors, placement and routingtools, layout compaction tools, and standard cell generators etc. Thetool collection (501) uses anisotropic design rules (502) to restrictthe relative positioning of polygon edges based on the orientation ofthe edge.

In a preferred embodiment, FIG. 6 shows a flow diagram for generatinglayout for an anisotropic image system. The steps performed in FIG. 6uses a subset of the tool collection 501.

During floor planning (602) and placement (603), a preferred orientationof the image system is used to optimize the shape, position andorientation of the circuit building blocks. More circuit element can beaccommodated in the direction with higher resolution, while thedirection with lower resolution has lower line-to-line parasiticcapacitance and lower resistance. In routing modules 604 and 605, wiringdirection dependent design rules from the memory are used foridentifying obstacles, setting wire width and spacing, and estimatingresistance and capacitance.

FIG. 7a shows a basic operation during wire routing. A wire isconstructed by the routing algorithm to connect two points, A and B. Ina preferred embodiment, starting from point A, while the wire is runninghorizontally (700), the application fetches the minimal width of thehorizontal wire from the memory and applies it to limit the current wiresegment. After turning 90 degrees (701), the wire now is running alongthe vertical direction, the application fetches the minimal width of thevertical wire from a different memory location and applies it to limitthe minimal line width.

The wire is also kept at safe distances away from obstacles 703 and 704using directional dependent minimal spacing rules. In a preferredembodiment, the layout generation system compares the separation 705between vertical line segments 701 and 704, with the minimal spacingrule between vertical lines and reports error when this horizontalconstraint is violated. Said system compares the separation 706 betweenhorizontal line segments 702 and 703, with the minimal spacing rulebetween horizontal lines and reports error when this vertical constraintis violated. In prior art physical design systems the minimal values for705 and 706 are the same and equal to the minimal space rule, which iskept at the same memory location in the design system.

FIG. 7b illustrates the procedure for wire jog insertion. In layoutsystems, interconnect needs to be converted from paths that have nowidth information to actual layout wires. The preferred width isspecified in the technology file. In a preferred embodiment, two numbersrepresenting preferred wire width in vertical and in horizontaldirection are read from different input fields. During path to wireconversion, the main wire portion 708 uses width and spacing width forthe vertical wires, while jog portion 707 uses width and spacing rulesfor horizontal wires.

In another preferred embodiment, design rule verification and compactionprograms in FIG. 6 are constructed to accept and process anisotropicdesign rules. For example, the corner to corner constraint on a layoutlayer my now be expressed as sqrt(d_h*d_h+d_v*d_v), where d_h and d_vate horizontal and vertical constraint distances respectively. Incontrast, in an isotropic layout system, said corner constraint issqrt(2)*d0, where d0 is the isotropic constraint distance.

Referring to FIG. 8, a block/flow diagram is shown for a system 800 ofthe present invention. System 800 includes a processor 802 that accessesmemory device 804. Memory device 804 stores an application softwarepackage 806 for implementing the present invention. A user interfaceswith the processor 802 through an input device 808 which may include akeyboard, a mouse, a touch screen monitor, a voice recognition system orother known input devices. A display 810 is also included to displayresults, prompts, user inputs, graphics, etc.

While the present invention has been described in detail with regards tothe preferred embodiments, it should be appreciated that variousmodifications and variations may be made in the present inventionwithout departing from the scope or spirit of the invention. In thisregard, it is important to note that practicing the invention is notlimited to the applications described hereinabove. Many otherapplications and/or alterations may be utilized if such otherapplications and/or alterations do not depart from the intended purposeof the present invention.

It should further be appreciated by a person skilled in the art thatfeatures illustrated or described as part of one embodiment can be usedin another embodiment to provide yet another embodiment such that thefeatures are not limited to the specific embodiments described above.Thus, it is intended that the present invention cover suchmodifications, embodiments and variations as long as such modifications,embodiments and variations come within the scope of the appended claimsand their equivalents.

What is claimed is:
 1. An integrated circuit product prepared by aprocess comprising the steps of: receiving a design layout comprising aplurality of layout objects residing on a plurality of layers; receivingdescriptions of a manufacturing process; constructing a system ofinitial constraints among said layout objects; computing one or morelocal process modifications to change said initial constraints usingsaid descriptions of manufacturing process; constructing new localconstraint distances by combining said local process modifications withconstraint distances in said system of initial constraints; enforcingsaid new local constraint distances; updating the coordinate variablesof said layout objects according to the solutions obtained fromenforcing said new local constraint distances, thereby obtaining updatedcoordinate variables of said layout objects; and fabricating theintegrated circuit product in accordance with the updated coordinatevariables, wherein the integrated circuit product comprises a firstplurality of routing wires running in a first direction, and a secondplurality of routing wires running in a second direction, the seconddirection being orthogonal to the first direction, the routing wires ofthe first plurality of routing wires having first width values, therouting wires of the second plurality of routing wires having secondwidth values, the first width values being substantially different fromthe second width values.
 2. The integrated circuit product of claim 1,wherein the process further checking said design layout against designrules.
 3. The integrated circuit product of claim 1, wherein the step ofcomputing one or more local process modifications comprises simulatingthe fabrication process selected from the group consisting of:lithography and etching.
 4. The integrated circuit product of claim 1,wherein the step of computing one or more local process modificationscomprises computing a distance of a modification from simulatedcontours.
 5. The integrated circuit product of claim 1, wherein the stepof enforcing said new local constraint distances comprises modifying oneor more distances between layout objects of the plurality of layoutobjects.
 6. The integrated circuit product of claim 1, wherein the stepof receiving initial a design layout comprises receiving one or morelayouts selected from the group consisting of: layouts of standardcells, layouts of memories, layouts of metal routing layers, layouts ofinput circuits, and layouts of output circuits.
 7. The integratedcircuit product of claim 1, wherein the step descriptions of themanufacturing process are selected from the group consisting of: designrules, simulation models, equipment settings, material selections, andlook up data tables.
 8. The integrated circuit product of claim 1,wherein the step of constructing comprises constructing constraints fromdesign rules.
 9. The integrated circuit product of claim 1, wherein saidstep of computing one or more local process modifications comprisesdetecting processing hotspots.